Currently, the Third Generation Partnership Projects (3GPP) launched a standard of the Long-Term Evolution advance (LTE-Advanced). The LTE-Advanced which is a relative improvement of Long-Term Evolution (LTE) retains the core of LTE, based on which a series of technologies are used to extend the frequency domain and space domain so as to improve utilization rate of spectrum, increase capacity of system or the like. The wireless relay is one of the LTE-Advanced technologies and is intended to expand the coverage of the cell, reduce the corner areas in the communication, balance the load, transfer the services of the hotspot areas, and save the transmission power of the terminal (or namely user equipment, abbreviated as UE).
FIG. 1 is a schematic diagram of the network architecture using the wireless relay technology according to the prior art. As shown in FIG. 1, some new Relay Nodes (RNs) are added between the original Donor eNodeB (Donor-eNB) and UE, and these newly added RNs are wirelessly connected to the Donor-eNB, but are in the wired connection with the transmission network, wherein the radio link between the Donor-eNB and the RN is called as backhaul link and the radio link between the RN and the UE is called as access link. The downlink data first arrives at the Donor-eNB and then are transmitted to the RN, and afterwards the RN transmits it to the UE. The uplink data has the process inverted with the downlink data, which is not described in detail herein.
In order to configure resource of the backhaul link, Relay Physical Downlink Control Channel (R-PDCCH), Relay-Physical Dedicated Downlink Shared Channel (R-PDSCH), and Relay Physical Uplink Shared Channel (R-PUSCH) are defined. The resource of R-PDCCH, starting from an Orthogonal Frequency Division Multiplexing (OFDM) symbol received by the RN, can be partial Physical Resource Blocks (PRBs) in a subframe used for the downlink transmission of the backhaul link, or can also be partial OFDM symbols or all the OFDM symbols in a subframe used for the downlink transmission of the backhaul link.
FIG. 2 is a schematic diagram of the frame structure of a subframe used for the downlink transmission of the backhaul link according to the prior art. As shown in FIG. 2, the R-PDCCH is used to allocate an R-PDSCH resource and an R-PUSCH resource dynamically or semi-statically, wherein the R-PDSCH resource is used to transmit the downlink data of the backhaul link and the R-PUSCH resource is used to transmit the uplink data of the backhaul link. Considering the compatibility with the existing terminals and in order to avoid the transmission between the relay node and the base station has conflict with the transmission between the relay node and the terminal, the relay node monitors during normal transmission process the Downlink Assignment, Uplink Grant and the like which are indicated by the base station on the R-PDCCH, and then achieves the transmission between the relay node and the base station on the corresponding R-PDSCH and R-PUSCH. In addition, the relay node indicates Downlink Assignment, Uplink Grant and the like on Physical Downlink Control Channel (PDCCH) and achieves the transmission between the relay node and the terminal on the corresponding Physical Downlink Shared Channel (PDSCH) and Physical Uplink Shared Channel (PUSCH).
Before the normal transmission process, the relay node in idle state (RRC_IDLE) needs to initially access the network by a random access procedure, and the relay node in the connected state (RRC_CONNECTED) needs to synchronize with the network and acquire resource allocation by the random access procedure so as to carry out subsequent data communication.
In a LTE system, the random access procedure can be triggered by any one of the following five events: (1) initial access in idle state; (2) initial access after Radio Link Failure (RLF); (3) Handover (HO); (4) downlink data being arrived in the connected state; and (5) uplink data being arrived in the connected state. Moreover, there are two different manners of the random access procedure: Contention Based (which is applicable for all the above five events); and Non-contention Based (which is only applicable for the above two events (3) and (4)). After the random access procedure is successful, normal downlink or uplink transmission can be carried out.
FIG. 3 is an interacted flow chart of the random access procedure in the manner of Contention Based according to the prior art. As shown in FIG. 3, the random access procedure in the manner of Contention Based comprises the following four steps.
Step 1: a terminal sends a random access preamble through Random Access Channel (RACH) in uplink.
Step 2: the Media Access Control (MAC) layer of base station generates a Random Access Response (RAR) message and sends the generated RAR message to the terminal through DownLink Shared Channel (DL-SCH), wherein the RAR message at least contains Random Access Preamble Identifier (RAPID), Time Alignment (TA) information, initial Uplink Grant (UL Grant) and temporary Cell-Radio Network Temporary Identifier (Temporary C-RNTI); and the RAR message is indicated by Random Access-Radio Network Temporary Identifier (RA-RNTI) on the Physical Downlink Control Channel (PDCCH).
Step 3: the terminal sends a first Scheduled Transmission message on the Uplink-Shared Channel (UL-SCH), wherein the content of the Scheduled Transmission message at least contains Cell-Radio Network Temporary Identifier (C-RNTI) Media Access Control element (MAC Control Element) or Common Control logic Channel Service Data Unit (CCCH SDU); and the process of sending this Scheduled Transmission message can be supported by the Hybrid Automatic Retransmission reQuest (HARQ).
Step 4: the base station sends a Contention Resolution message on the DL-SCH,
wherein the Contention Resolution message is indicated by the C-RNTI or the Temporary C-RNTI on the PDCCH, and the process of sending this Contention Resolution message can be supported by the HARQ.
FIG. 4 is a random access procedure in the manner of Non-contention Based. As shown in FIG. 4, this random access procedure comprises the following steps.
Step 1: a base station allocates a random access preamble to a terminal through a downlink dedicated signaling,
wherein in the situation of handover, the downlink dedicated signaling is generated by a target base station and sent to the terminal by a source base station using a Handover (HO) Command; and in the situation that the downlink data arrives, the downlink dedicated signaling is sent to the terminal through the PDCCH.
Step 2: the terminal sends the allocated non-contention random access preamble through the RACH in uplink.
Step 3: the base station sends the RAR message on the DL-SCH, wherein the RAR message at least contains time alignment information and the RAPID, and in the situation of handover, the RAR message further contains the UL Grant, and the RAR message is indicated by the RA-RNTI on the PDCCH.
After the random access procedure is successful, the terminal monitors the PDCCH and acquires Downlink Assignment or Uplink Grant and the like by the C-RNTI indication on the PDCCH, then performs corresponding downlink transmission or uplink transmission. It can be seen from the above-mentioned that if the RN uses the random access procedure of the terminal, the RN will monitor the PDCCH after the access is successful. The subsequent transmission can't be carried out normally.
For the problem of how the RN accesses the R-PDCCH and performs the subsequent transmission normally, no effective solution has been proposed so far.